sw.js

self.addEventListener('install', e => {
  self.skipWaiting()
})

self.addEventListener('activate', evt => {
  return self.clients.claim()
})

self.addEventListener('fetch', evt => {
  const { request } = evt
  const { url, method, headers } = request

  if (!url.includes(self.registration.scope + 'webtorrent/')) return null

  console.log("url", url)

  // keep the worker alive
  if (url == `${self.registration.scope}webtorrent/ping`) {
    evt.respondWith(new Response("pong", { status: 200 }))
    return
  }

  function getConsumer(clients) {
    return new Promise(resolve => {
      // Use race condition for whoever controls the response stream
      for (const client of clients) {
        const mc = new MessageChannel()
        const { port1, port2 } = mc
        port1.onmessage = evt => {
          resolve([evt.data, mc])
        }
        client.postMessage({
          url,
          method,
          headers: [...headers],
          scope: self.registration.scope
        }, [port2])
      }
    })
  }

  evt.respondWith(
    clients.matchAll({ type: 'window', includeUncontrolled: true })
      .then(getConsumer)
      .then(([data, mc]) => {
        let tm = null
        const body = data.body === 'stream'
          ? new ReadableStream({
            pull(controller) {
              return new Promise(resolve => {
                mc.port1.onmessage = evt => {
                  if (evt.data) {
                    controller.enqueue(evt.data) // evt.data is Uint8Array
                  } else {
                    clearTimeout(tm)
                    controller.close() // evt.data is null, means the stream ended
                    mc.port1.onmessage = null
                  }
                  resolve()
                }
                // 'media player' does NOT signal a close on the stream and we cannot close it because it's locked to the reader,
                // so we just empty it after 5s of inactivity,
                // the browser will request another port anyways
                clearTimeout(tm)
                tm = setTimeout(() => {
                  controller.close()
                  mc.port1.postMessage(false) // send timeout
                  mc.port1.onmessage = null
                  resolve()
                }, 5000)
                mc.port1.postMessage(true) // send a pull request
              })
            },
            cancel() {
              // This event is never executed
              mc.port1.postMessage(false) // send a cancel request
            }
          })
          : data.body

        return new Response(body, data)
      })
      .catch(console.error)
  )
})